The invention relates to soil cultivation apparatus for cultivating rice and other crops, and to methods which allow the apparatus to cultivate moist or dry earth to remove weeds from within a growing stand of rice. The apparatus of the invention can be used with any crop which is planted three-fourths of an inch or deeper into the soil.
Soil cultivating apparatuses are well known in the art. Such apparatuses are used for seedbed preparation before planting, or to remove weeds from between rows of actively growing crops. For example, a rotary harrow having a plurality of spaced soil working tines is disclosed in U.S. Pat. No. 4,171,725. An adjustable tooth harrow is disclosed in U.S. Pat. No. 2,730,854 which has a series of drag bars, each with teeth which can be adjusted either forward or backward. Spring tooth harrows are disclosed in U.S. Pat. Nos. 3,049,184 and 3,016,958. These references describe cultivating implements with spring or flexible teeth and a tooth mounting means providing a frictional snubbing action to reduce tooth breakage.
Currently, there are two methods of producing paddy rice in the United States. The conventional method in California is to aerially "broadcast" the rice seed into pre-cultivated and pre-flooded paddies that remain flooded for the entire growing season, except for brief periods required for usage of certain pesticides. Between April and early June, the paddy seedbed is prepared by chisel plowing and discing. The ground is leveled with the use of a triplane. The goal is to produce a level paddy with a soil clod size of about two inches in diameter. Nitrogen fertilizer in amounts of 100 units or more per acre is applied to the paddy, either aerially or with equipment pulled by tractors, and incorporated into the soil. A starter fertilizer containing phosphorus and trace elements is also often used. Fertilizer amounts are usually based on the results of soil analysis. Seed is usually treated with a fungicide or pelletized (containing micronutrients). 100 to 200 pounds of seed is aerially broadcast over the flooded paddy. The seed germinates, becomes rooted in the soil, and the plants grow above the water level in the paddy. Herbicides are applied to the fields to control weeds. To control grass weeds, the herbicide Ordram.RTM. may be aerially broadcast before flooding and incorporated into the upper one to two inches of soil. This chemical may also be combined with the irrigation water as it is added to the paddy, or it may be aerially applied after flooding. The herbicides Ordram.RTM. and Bolero.RTM. are used to control grass weeds. Broadleaf weeds may be controlled with the use of Basagram.RTM. or MCPA (2-methyl-4-chlorophenoxyacetic acid). Their use requires the paddy to be drained, and these chemicals are then sprayed or broadcast onto the field. Insecticides are used to control insect pests that damage the rice plants. To control rice weevils, Furadan.RTM. is broadcast and incorporated into the soil along the edges of the field and on the levees prior to flooding. After flooding, Furadan.RTM. is applied by draining the paddy and broadcasting the chemical but without incorporation into the field. Algae growth and tadpole shrimp are controlled by broadcasting copper sulfate into the flooded paddy. Leaf miners, rice midge and tadpole shrimp may be controlled by broadcasting methyl or ethyl parathion into the flooded paddy.
The rice paddy is normally flooded to a water level of four to sic inches in depth prior to planting. This water level is maintained throughout the growing season, except when the paddy is derained to allow any required herbicide or pesticide treatments, or the water level is increased to protect pollen from cold weather during the "boot" stage of growth.
The second method of growing paddy rice, predominately used in the southern United States, involves use of the same seedbed preparation. A conventional grain drill is used to plant 60-80 pounds of seed into the upper half-inch of dry soil. The rice paddy is then shallowly flooded with water. After germination and emergence of the seedlings, soil moisture is retained by occasional irrigation flushing until permanent flooding is conducted, after the fourth leaf development of the seedlings. Herbicide and pesticide treatments are the same as in the first method. Both methods can be modified for use in organic farming by using natural fertilizers and by deeper flooding (8-12 inches of water) to aid in weed control. However, a reduced yield usually results with organic modifications.
Research on rice sowing depth and time between irrigation and sowing has been reported in Hanviriyapant et al., Field Crops Res. 16, 273 (1987). Rice was drilled 6-8 cm deep into moist soil in northwest Australia. Weeds, which germinated following the single irrigation prior to planting, were controlled by cultivation just before planting. The cultivation of rice once the stand is established creates special problems, such as removing weeds without damaging or uprooting the rice plants.
Rice has been grown previously in a semi-moist (muddy) environment. However, such an environment allows the rapid and profuse growth of weeds, which must then be removed before or during the early growth stage or the yield of rice will be seriously reduced. Insects and other pests also damage rice plants, and in normal practice, herbicides and pesticides are used to eliminate unwanted weeds and insects. However, it can be appreciated that such use of herbicides and pesticides undesirably affects water quality and wildlife, and increases overall crop production costs. In some areas, water from rice farms treated with pesticides is discharged into other bodies of water, which is also highly undesirable. Legislation has been enacted in some parts of the United States to reduce or eliminate the use of pesticides and to control discharges of water from areas so treated.
A need exists for a mechanical means for weed control during rice crop production and a method for growing rice that will result in satisfactory rice yields and yet eliminate or reduce the use of environmentally hazardous herbicides and pesticides. This can be accomplished by using an other-than-normal planting depth and by changing the schedule of irrigation, which results in differences in plant size and vigor between rice and weeds. It also controls the environment for the insects and other pests, interrupting their life cycles. The apparatus of the invention successfully cultivates the rice on the basis of these differences. The process of growing rice of the invention provides conditions under which weeds and rice pests are controlled in the field. An increased tillering of the rice plants also occurs, holding per-acre yields to the same levels previously obtained by existing (conventional) methods.